1. Field of the Invention
This invention relates to a dentifrice which provides a user perceivable signal of cleaning efficacy or a "prophy mouthfeel" in the oral cavity during and after use in teeth cleaning.
2. The Prior Art
Among the desirable oral sensations obtained by the use of dentifrices in the cleaning of teeth is "prophy mouthfeel" or a "dentist clean" mouth sensation. This is the same sensation one feels during and after a professional dental prophylaxis and is conveyed in a dentifrice by the polishing agent contained in the dentifrice. The mouthfeel, described as "gritty" or "crunchy", by the user is advantageous as it sends an extra signal of proof of efficacy that the dentifrice is doing more than an ordinary dentifrice.
A dentifrice known to the art to deliver a prophy mouthfeel to the user is described in U.S. Pat. No. 4,401,648. The polishing agent primarily responsible for the prophy mouthfeel is a hydrated alumina product having a particle size wherein 100% of the particles are less than 50 microns and 84% of the particles are less than 20 microns.
In consumer product evaluation tests in which panelists were asked to compare their current brand of toothpaste to the dentifrice of U.S. Pat. No. 4,401,648, the dentifrice was rated significantly higher in "cleaning teeth better".
Although the dentifrice of U.S. Pat. No. 4,401,648 exhibits strong positive ratings with respect to mouthfeel, the dentifrice had the drawback that it exhibits relatively high abrasion values, e.g. 150 units or more when subjected to Radioactive Dentin Analysis (RDA). "RDA" value is obtained by first irradiating extracted teeth in a neutron flux to make them radioactive and then brushing a dentin surface of the tooth, under standard conditions of brushing, and determining the radioactivity of the slurry surrounding the teeth after their removal.
Dentifrices having RDA values in excess of 150 raise the concern that continued use of such dentifrices will damage oral hard tissues (enamel, dentin and cementum), particularly the dentin surfaces. A second drawback to the dentifrice of U.S. Pat. No. 4,401,648, is that the stability and efficacy of certain fluoride anticaries agents advantageously incorporated in dentifrices, e.g. sodium and tin fluoride, is adversely affected by the presence of the alumina polishing agent. Therefore, it would be advantageous to formulate a dentifrice composition containing a polishing agent which would impart prophy mouthfeel with low RDA values and be compatible with a broad spectrum of fluoride anticaries agents including sodium and tin fluoride.
Siliceous polishing agents are known to be compatible with fluoride anticaries agents such as sodium and tin fluoride when incorporated as abrasives in dentifrices. U.S. patents disclosing dentifrices formulated using siliceous polishing agents include U.S. Pat. Nos. 3,689,637; 3,943,240; 3,978,205; 4,007,260; 4,108,978; 4,110,083; 4,141,969; 4,144,322; 4,663,153; 4,469,216; 4,828,833; 4,891,211 and 4,943,429.
U.S. Pat. No. 3,689,637 discloses a dentifrice composition comprised of a high molecular weight polyethylene glycol, a humectant, a silica xerogel, silica aerogel and a pyrogenic silica. The silica xerogel has an average particle diameter of 2-20 microns, the silica xerogel has an average particle diameter of about 1-3 microns and the pyrogenic silica has an average particle diameter of 15 millimicrons. The silica xerogel is present in the dentifrice at a concentration of 5-50% and the silica aerogel and/or the pyrogenic silica is present at a concentration of 0.5-20% percent.
U.S. Pat. No. 3,943,240 discloses a toothpaste containing sodium bicarbonate as the principal abrasive and a lesser amount of another compatible abrasive such as crystalline or amorphous silica having a particle size less than about 20 microns.
U.S. Pat. No. 3,978,205 discloses a dentifrice containing dehydroxylated fumed silica having a particle size of about 10-100 millimicrons.
U.S. Pat. No. 4,007,260 discloses a translucent dental cream containing finely divided synthetic amorphous silica having a particle size of about 1-30 microns.
U.S. Pat. No. 4,108,978 discloses a dentifrice containing 1-50% by weight of a silica xerogel having an average particle size of 25-50 microns.
U.S. Pat. No. 4,110,083 discloses a dentifrice having an abrasive coated with a cationic water soluble polymer whereby the abrasive is made less absorptive to therapeutic cationic agents. Illustrative of abrasives suitable for use in the dentifrice include silica xerogels having an average particle size of 1-30 microns.
U.S. Pat. No. 4,141,969 discloses a dentifrice containing a compound which provides fluoride (N.sub.a F, S.sub.n F.sub.2), an amorphous silica polishing agent having an aggregate particle size of 2-20 microns and an additive which supplies calcium ions.
U.S. Pat. No. 4,663,153 discloses a tooth powder comprised of at least 50% by weight of sodium bicarbonate particles having a median particle size of 74-210 microns. Secondary abrasives such as silica gel (hydrated silica) having a particle size of 8-13 microns may also be incorporated in the dentifrice.
U.S. Pat. No. 4,689,216 discloses dentifrices containing sanguinarine of superior stability and increased uptake into dental plaque are attained by the inclusion of hydrated silica as an abrasive.
U.S. Pat. No. 4,828,833 disclose dentifrice compositions containing a siliceous dental abrasive such as amorphous precipitated silica having a particle size less than 20 microns to avoid any gritty feel.
U.S. Pat. No. 4,891,211 discloses a hydrogen peroxide-releasing dentifrice comprising a sodium bicarbonate and sodium percarbonate in a polyethylene glycol base. The sodium bicarbonate abrasive has a particle size less than about 25 microns and the median particle size is desirably less than 44 microns. Amorphous silica is included as a secondary abrasive.
U.S. Pat. No. 4,943,429 discloses a sodium bicarbonate based dentifrice gel which comprises sodium bicarbonate in an aqueous carrier with a humectant such as glycol or sorbitol. The sodium bicarbonate has a mean particle size of from 10-200 microns. Secondary abrasives such as silica gels may also be incorporated in the dentifrice gels.
A major drawback to the use of siliceous polishing agents at the concentrations, e.g., 15 to 25% by weight conventionally used in dentifrices is that at the particle size range at which a prophy mouth feel is imparted by the presence of these particles, i.e., in the 40 to 100 micron particle size range, the RDA values of the dentifrice very often exceed 150 units.
Therefore, there is a need in the art for a dentifrice which imparts a prophy mouth feel without being unduly abrasive and in which the ingredients thereof are compatible with alkali metal fluoride anticaries agents.